1. Field of the Invention
The present invention relates to a method of manufacturing a fluid-filled cylindrical damping assembly, and more particularly to an advantageous method of manufacturing a fluid-filled cylindrical damping assembly which is capable of exhibiting a damping effect on the basis of flows of a fluid therein advantageously with respect to inputted vibrations applied in an axial direction and which may be preferably used as a member mount for a suspension system of an automobile, for example.
2. Description of the Related Art
Conventionally, there is known a so-called fluid-filled cylindrical damping assembly, constructed such that a far excellent damping characteristic can be exhibited on the basis of flows such as resonance or the like of a fluid therein. Such a fluid-filled cylindrical damping assembly is interposed between two members constituting a vibration transmitting system, and known as a kind of damping assembly forming a damping connection of both the members. (refer to JP-A-5-332393).
In the conventional fluid-filled cylindrical damping assembly, for example, an intermediate sleeve (outer cylindrical member) disposed radially outwardly of a shaft member with a suitable distance and the shaft member to be attached to one of the two members in the vibration transmitting system configured to form the damping connection, are connected via a main elastic rubber body disposed therebetween, and an outer cylindrical metal member (outer-inserting cylindrical metal member) to be attached to the other of the two members, to be configured to form the damping connection, is inserted on the outer circumferential surface of the intermediate sleeve via a thin-walled sealing rubber layer which is disposed on an inner circumferential surface of the outer cylindrical metal member, and is fitted and fixed to the intermediate sleeve. A plurality of pocket portions opened in an outer circumferential surface are formed in the main elastic rubber body, and by means of that the openings of the pocket portions is covered with the outer cylindrical metal member, a plurality of fluid chambers filled with a non-compressible fluid whose at least a part of wall is defined by the main elastic rubber body and the sealing rubber layer are provided between the outer cylindrical metal member and the shaft member. The thus described fluid-filled cylindrical damping assembly is used as a member mount for a suspension system of an automobile, a strut bar cushion, a suspension upper support, or the like, for example.
In the conventional fluid-filled cylindrical damping assemblies described above, there has been disclosed a structure in which, while an inner flange portion is integrally formed at one end portion of one side in an axial direction of the outer cylindrical metal member, an engaging portion radially inwardly bent in a radial direction is provided at an end portion of the other side thereof, and in which each of the inner flange portion and the engaging portion is in engagement with both side end portions of an intermediate sleeve in an axial direction, respectively. (for example, refer to JP-A-10-47420) In the thus described fluid-filled cylindrical damping assembly, resistance force against extracting or pulling out force in the axial direction applied between the outer cylindrical metal member and the intermediate sleeve, namely extraction-resisting force in the axial direction of the outer cylindrical metal member and the intermediate sleeve can sufficiently be secured.
When the thus described fluid-filled cylindrical damping assembly is manufactured, in general, an intermediate molded-body in which the shaft member and the intermediate sleeve are connected by the main elastic rubber body is formed first. Further, the outer cylindrical metal member is formed in which the inner flange portion is integrally formed at the end portion of one side in the axial direction, and the thin-walled sealing rubber layer is disposed on the inner circumferential surface. Then, the outer cylindrical metal member is inserted on an outer circumferential surface of the intermediate molded-body, in the non-compressible fluid, and an inside surface of the inner flange portion of the outer cylindrical metal member is brought into contact and engaged with an end surface of one side of the intermediate sleeve in an axial direction, and to be in engagement therewith, and thus, the outer cylindrical metal member and the intermediate molded-body are assembled. Thereafter, a diameter-reducing operation such as an eight drawing dies or the like is performed for the outer cylindrical metal member so that the outer cylindrical metal member is fitted on and fixed to the intermediate sleeve. An end portion of the outer cylindrical metal member at a side opposite to the side, at which the inner flange portion is caused to be radially inwardly bent and the engaging portion is formed at the end portion. The engaging portion is engaged with the end portion of the intermediate sleeve. Thus, the intended fluid-filled cylindrical damping assembly is obtained.
Under the aforementioned condition, the inventors of the present invention have made a study on the conventional fluid-filled cylindrical damping assembly from various angles. As a result, it becomes apparent that in the conventional fluid-filled cylindrical damping assembly, a manufacturing efficiency is inevitably deteriorated in mass production.
That is, in a case that the fluid-filled cylindrical damping assembly is mass-produced by the conventional manufacturing method as described above, ordinarily, a plurality of outer cylindrical metal members are set to one vulcanization mold, and in this condition, sealing rubber layers are vulcanized on the inner circumferential surfaces of the respective outer cylindrical metal members at the same time. At this moment, since the inner flange portion is provided at one end portion in the axial direction of the outer cylindrical metal member, a portion of the mold intruded in a center hole of the outer cylindrical metal member has to be extracted only from the other side in the axial direction of the outer cylindrical metal member, when the sealing rubber layer is demolded after performing the vulcanization-molding operation. Therefore, sliding resistance between an outer circumferential surface of the portion of the mold and the inner circumferential surface of the outer cylindrical metal member becomes extremely large. As a result, the demolding operation for the outer cylindrical metal member from the mold for vulcanization becomes difficult and causes a below mentioned problems. That is, the manufacturing efficiency for forming the plurality of outer cylindrical metal members at one time and the manufacturing efficiency in the mass production for producing the intended fluid-filled cylindrical damping assembly are deteriorated.
To solve these problems, the inventors of the present invention have made an idea to apply an extracting or pulling out slope to the outer cylindrical metal member by means of forming the same having a tapered cylindrical shape where a diameter thereof is gradually increased along the axial direction from one side to the other side. That is, a demolding capability of the outer cylindrical metal member can be increased by applying the extracting slope.
Although the manufacturing efficiency for the outer cylindrical metal member is certainly increased due to the improvement of the demolding capability when the fluid-filled cylindrical damping assembly is practically manufactured using the outer cylindrical metal member having the tapered cylindrical shape, the main elastic rubber body constituting a part of the wall portion of the fluid chamber is partially expanded when the outer cylindrical metal member is inserted on the outer circumferential surface of the intermediate molded-body in the non-compressible fluid, and the diameter-reducing operation on the outer cylindrical metal member is performed after assembling the same in a manufacturing process for the intended fluid-filled cylindrical damping assembly. Thereby, it becomes clear that a bad influence is affected to a damping characteristic or durability, and further that there may be caused damage at the expanded portion of the main elastic rubber.